Electronics products are increasingly being provided for installation in vehicles. Typically, such products draw power from the vehicle's electrical system and therefore product operation depends on the vehicle's ability to provide energy to the product. When the vehicle's engine is turned on, the alternator provides electricity with significantly less limitation than when the engine is turned off. When the engine is turned off, electricity is supplied instead via the vehicle's battery, which is significantly more limited (for example in that the battery's supply of stored energy is less than the supply of energy stored as fuel and available as electricity through operation of the vehicle's engine and alternator). Products powered by the vehicle's electrical system can therefore be made to switch to a low power mode to avoid prematurely discharging the vehicle's battery when the engine is off.
To realize this function, the device may be configured to monitor the battery voltage in order to infer the vehicle's engine status. For example, when the vehicle engine is turned off, the battery voltage may fall within a first range, for example of about 12 V. When the vehicle engine is turned on, the battery voltage may fall within a second range, for example of about 14 V. Absolute battery voltage may significantly vary around the values indicated above, depending on vehicles type and battery aging.
It is noted that monitoring of the power system also requires power, and therefore it is desired that monitoring operations should also consume low amounts of power so that they themselves do not prematurely discharge the battery. One solution is based on a dual-processor architecture as follows. When the vehicle's engine is off, a main processor is inactive or idle, and the vehicle's power system monitoring is managed by a second, lower-powered digital microprocessor. The power system voltage is sampled at a sufficient rate, for example via an analog-to-digital converter (ADC) and the lower-powered processor wakes up the main processor if the vehicle's engine is detected to turn on. However, this solution incurs the expense of an additional processor and still requires significant power in order to operate the ADC and lower-powered processor during standby.
Therefore there is a need for a method and apparatus for adapting to limitations in a power source that is not subject to one or more limitations of the prior art.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present technology. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present technology.